It would be interesting to see a microvm (kata/firecracker/etc.) version of vagrant. And open source, of course. I can't see any technical reason why it would be particularly difficult.
I don't think they're that valuable tbh. Outside of cases where you're running completely untrusted code or emulating a different architecture, there's no strong reason to pick any VM over one of the several container paradigms.
One more usecase - which I admit is niche - is that I want a way to run multiple OSs as transparently as possible. A microvm that boots freebsd in less than a second and that acts almost like a native container would be excellent for certain development work.
Edit: Actually it's not just cross-OS work in the freebsd/linux sense; it would also be nice for doing kernel dev work. Edit my linux kernel module, compile, and then spawn a VM that boots and starts running tests in seconds.
